1. Technical Field
The present invention relates to light-emitting diode (LED) based lighting tubes, and in particular to LED based lighting tubes for serving as replacements for fluorescent lighting tubes.
2. Background Art
LED lighting tubes have for many years been used as energy efficient replacements for conventional fluorescent lighting tubes. A typical LED lighting tube includes an LED assembly enclosed at least partially within a clear or frosted tubular envelope. The LED assembly includes a plurality of LEDs in electrical connection with a circuit board, which is usually attached to a heat sink or other heat dissipating device. The open ends of the tubular envelope are usually closed by end caps, which also provide electrical connection between the LED assembly and a power supply.
The mounting of the LED assembly within the tubular envelope engenders problems that have not been solved in the prior art. In many exemplary lighting tubes, such as those disclosed in U.S. Pat. No. 7,510,299 to Timmermans, et al., and U.S. Pat. No. 7,053,557 to Cross, et al., the LED assembly is attached to supports that are suspended from the end caps or from the interior of the envelope. This configuration is costly to construct and difficult to keep in proper alignment during shipping and installation of the LED lighting tube. It also limits the arc of illumination, since light emitted by the LEDs is blocked by the supporting structures, the circuit board, and the heat sink. In other exemplary lighting tubes, such as that disclosed in U.S. Pat. No. 7,815,338 to Siemiet, et al., the LED assembly interrupts the circumference of the tubular envelope, with the heat sink being situated outside of the envelope. In cross section, the envelope forms an incomplete circle, with free edges attaching to the heat sink or to another part of the LED assembly. This type of design excludes the use of desirable but delicate envelope materials such as thin glass or brittle plastic, because it is difficult or impossible to durably attach their free edges to the LED assembly without breakage. The design also limits the arc of emitted light with the bulky opaque structure of the heat sink. There is a need for an LED lighting tube of light and simple construction.
LED lighting tubes, and lighting tubes of all types, typically include a frosted film on the tubular envelope, to diffuse and reduce the harshness of the emitted light. Typical films include paints or powders, which are difficult to apply evenly, and which provide no mechanical protection for the envelope. There is a need for a lighting tube film that is readily applied in a consistent manner, and which protects the lighting tube.